The present invention provides a novel and reliable method for detecting when a subject responds deceptively.
Current technology for detecting deception is typified by the polygraph test which measures the activity of the subject""s autonomic nervous system (galvanic skin response, respiration rate, heart rate, etc.) in response to questions. Disadvantages of the polygraph test include that it does not directly measure brain activity associated with deception, and that the test is subject to countermeasures by a trained, knowledgeable and/or determined subject. In addition, the scientific basis and validity of the polygraph test is often challenged and results of polygraph tests are not admissible as evidence in court proceedings. Nevertheless, the polygraph test continues to be administered by various authorities.
Studies have attempted to demonstrate that the event-related brain potential (ERPs) can be used to detect deception in human subjects. These efforts have focused on developing ERPs, specifically the P300, a positive ERP component with a latency of at least 300 ms, as a tool to reveal when subjects possess certain information in their memory. For example the P300 has been used in the Guilty Knowledge Test (GKT), to detect if a subject possesses information related to a crime (U.S. Pat. No. 4,941,477 (Farwell); U.S. Pat. No. 4,932,416 (Rosenfeld)), or as a tool to detect memory deficiency malingering (U.S. Pat. No. 5,846,207 (Rosenfeld). This research however did not directly examine cognitive processes or brain activity related to the deception. A disadvantage of the GKT is that it indirectly assesses the presence of guilty knowledge and thus may be subject to countermeasures by the subject. In addition, because the GKT tests knowledge of a crime, it is not useful in the majority of polygraph tests, such as those used for screening employees or potential employees for security reasons and where commission of a crime is not at issue.
In non-deceptive situations, response conflict is typically induced when one aspect of a stimulus suggests one particular response while another aspect of the same stimulus suggests a different, competing response. Such situations can be classified as perceptually-driven response conflicts. One example is the Stroop test in which subjects see color words printed in different colored inks and are instructed to respond by naming the color of the ink in which a word is printed and to ignore the response indicated by the word itself. Perceptually-driven response conflicts affect task performance by reducing accuracy and slowing responses (Casey et al., 2000, Carter et al., 1998; Scheffers and Coles, 2000).
Studies of brain activity using functional magnetic resonance imaging (fMRI) have shown that the anterior cingulate cortex, an area of the medial frontal lobes, is active in situations when there is uncertainty about the proper response for a stimulus, such as when stimuli produce conflicting response tendencies (Botvinick et al., 1999; Casey et al., 2000; Carter et al., 1998, 2000). Therefore, it is believed that the anterior cingulate plays an important role in monitoring potential conflicts between intended and actual responses and signaling when a correction needs to be made (e.g., in situations when the response being prepared does not match the intended correct response)(Botvinick et al.,1999; Carter et al., 1998).
The error-related negativity (ERN) component of the ERP occurs between 0 to 100 ms after a response and is recorded maximally over medial central-frontal scalp. The ERN has been detected in tests in which the stimuli elicit conflicting response tendencies. While the largest ERNs have been found in error trials (Falkenstein et al., 2000), smaller ERNs are also found in correct trials (Vidal et al., 2000), particularly when degrading stimulus quality created uncertainty about how the stimulus should be categorized (Scheffers and Coles, 2000). Localization studies have placed the neural generator of the ERN in the medial frontal lobes, in or near the anterior cingulate cortex (Miltner et al., 1997) suggesting that the ERN may be linked with the activity measured in the anterior cingulate cortex fMRI studies cited above.
Little is known about the cognitive processes used when subjects are being deceptive and less is known about the brain activity underlying these cognitive processes.
It is thus an object of the invention to compare how the brain processes response conflicts in deceptive situations and non-deceptive situations.
It is an object of the present invention to provide a reliable method for testing deception that is less susceptible to the influence of countermeasures, is not dependent on the intent to deceive and detects long-term strategic deceptive patterns.
The present invention provides a method for determining whether a subject responds deceptively comprising a) presenting the subject with a test series of stimuli; b) presenting the subject with a control series of stimuli; c) monitoring the subject""s electrophysiological activity, behavioral activity, or both, associated with the subject""s response to the test series and control series of stimuli; d) comparing the subject""s electrophysiological activity, behavioral activity, or both, obtained from the responses to the test series and control series of stimuli; wherein a difference in the activity between the test and control stimuli indicates that the subject is responding deceptively.
The present invention also provides a method for determining whether a subject responds deceptively comprising a) presenting the subject with one or more sets of stimuli, each set comprising a test series of stimuli and a control series of stimuli; b) monitoring the subject""s electrophysiological activity, behavioral activity, or both, associated with the subject""s response to each set of stimuli; and c) comparing the subject""s electrophysiological activity, behavioral activity, or both, obtained from the responses to one set of stimuli to the activity from another set of stimuli; wherein a difference in the activity between the sets of stimuli indicates that the subject is responding deceptively. This embodiment is also known as a Repetition Series.
The present invention further provides a method for determining whether a subject possesses guilty knowledge comprising a) presenting the subject with a test series of stimuli wherein the test series of stimuli comprises an equal number of relevant and irrelevant items; b) presenting the subject with a control series of stimuli wherein the control series of stimuli comprises an equal number of relevant and irrelevant items; c) monitoring the subject""s electrophysiological activity, behavioral activity, or both, associated with the subject""s response to the test series and control series of stimuli; d) comparing the subject""s electrophysiological activity, behavioral activity, or both, obtained from the responses to the test series and control series of stimuli; wherein a difference in the activity between the relevant and irrelevant items indicates that the subject possesses guilty knowledge. This embodiment is also known as the guilty knowledge test.
According to the methods described herein, the electrophysiological activity comprises event-related brain potential (ERP); and behavioral activity comprises speed of response, variability in response speed and accuracy of response. The difference in electrophysiological and behavioral activity is defined by one or more markers, defined below which indicate when a subject is being deceptive or possesses guilty knowledge. The method of detecting deception described herein is suitable for both practiced and unpracticed deceptive responses. The method is independent of the subject""s intent to commit deception. The method also differentiates lies (e.g., saying one wasn""t in a place when they were there) from confabulations (e.g., saying one was in a place when they were not there).